S cam assembly

ABSTRACT

An S cam assembly, includes an S cam member having a shank, the shank having a machined shank outer margin, a tubular bushing holder member disposable annular to the shank, and a single S cam bushing member disposable intermediate the shank machined shank outer margin and an inside margin of the bushing holder when the bushing holder is in the annular disposition relative to the shank.

RELATED APPLICATIONS

This application is a continuation of application Ser. No. 10/673,641 filed Sep. 26, 2003, which claims the benefit of U.S. Provisional Application No. 60/454,744 filed Mar. 14, 2003, each of which is hereby fully incorporated herein by reference.

TECHNICAL FIELD

The present application relates to brake actuation. More particularly, the present application relates to a S cam assembly suitable for brake actuation.

BACKGROUND OF THE INVENTION

S cams are widely used in the commercial trucking industry. The S cam is an intermediary device between a pneumatic brake actuator and a set of wheel brakes. The S cam is typically an elongate metal rod or shank having an S-head at one end and a set of splines at the other end. The S-head has two opposed arms, generally defining an S shape. Each of the individual arms of the S-head engages a respective brake shoe. Rotation of the S cam causes the respective arms of the S-head to bear on a respective brake shoe, causing the brake shoe to frictionally engage the brake drum that is affixed to the wheel. In the past, the S cam has been rotationally supported by at least two bushings. A first bushing was positioned proximate the S-head and a second bushing was positioned proximate the splines.

The bushings have typically been exposed to the elements as the S cam is mounted exposed rearward of the axel of the vehicle. The intrusion of water, salt, and dirt into each of the bushings causes the bushings to fail in relatively short order. Replacement of the bushings is a necessarily frequent task that keeps the vehicle off the road for a significant period of time.

More recently, a Canadian company has provided a single tube that substantially encloses the elongate shank of the S cam and the two bushings.

There is a need in the industry to reduce the number of bushings that support the S cam and to provide for a longer service life of such bushing.

SUMMARY OF THE INVENTION

The present invention substantially meets the aforementioned needs of the industry. The number of bushings noted in the prior art is reduced to a single bushing. The single bushing of the present invention supports substantially the entire shank of the S cam from proximate the S-head to proximate the splines of the S cam. Preferably, the single bushing is enclosed within a full-length bushing holder. The bushing holder substantially encloses the bushing and provides end seals to isolate the single bushing from the environmental effects noted above including, moisture, salt, and road grit. The use of a single bushing and isolating the single bushing from the environment results in the single bushing requiring essentially no maintenance other than the occasional addition of lubrication. Accordingly, the down time for vehicles employing the S cam assembly of the present invention is greatly reduced.

The present invention is a S cam assembly, including a S cam member having a shank, the shank having a machined shank outer margin, a tubular bushing holder member disposable annular to the shank, and a single S cam bushing member disposable intermediate the shank machined shank outer margin and an inside margin of the bushing holder when the bushing holder is in the annular disposition relative to the shank.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded view of the S cam assembly of the present invention;

FIG. 1 a is an end elevational view of the bushing;

FIG. 1 b is an end elevational view of the bushing holder;

FIG. 2 is a sectional view of the bushing holder; and

FIG. 3 is perspective view of the S cam and S cam bushing assembly mated to a wheel brake.

DETAILED DESCRIPTION OF THE DRAWINGS

The S cam assembly of the present invention is shown generally at 10 in the Figures and includes generally S cam member 12, bushing member 40 and bushing holder member 42.

The S cam member 12 has a S-head 14 fixedly coupled to an elongate shank 16. When viewed end-on, the S-head 14 has a generally S-shape having two opposed arms 15 for engaging respective brake shoes in a brake assembly. Rotation of the S-head 14 relative to the brake shoes 17 in a first direction is effective for shifting the brake shoes 17 relative to an interior surface 11 of a brake drum 13 and thereby compressively, frictionally engaging the brake shoes 17 with the brake drum 13, as depicted in FIG. 3.

The shank 16 preferably has an elongate cylindrical shape. The shank 16 is preferably a solid metallic component that is usually forged or cast integral with the S-head 14. In the past, the outside margin of the shank 16 was left essentially as it was formed in a forging or casting operation with a generally irregular, rough surface with no particular O.D. dimension. With the present invention, the outside diameter 24 of the shank 16 is machined uniformly to a certain outside diameter having a substantially smooth surface.

As depicted in FIG. 1, a series of splines 18 are formed on the end of the shank 16 opposite to the S-head 14. A slack adjuster 20 having a splined insert 22 is adapted to engage the splines 18. The slack adjuster 20 is typically operably coupled by an adjustable link 17 to a pneumatic brake actuator 19. Linear motion imparted to a distal end of the slack adjuster 20 imparts rotational motion to the S cam member 12 for actuating the brakes of the vehicle, as indicated in FIG. 3. A plurality of washers 21 may be disposed on either side of the slack adjuster 20.

The S cam assembly 10 includes a further two major components, as noted above: bushing member 40 and bushing holder 42.

The bushing member 40 has an elongate tubular body 44. The tubular body 44 has a known outside diameter 46 and a known inside diameter 48, as depicted in FIG. 1 a. The inside diameter 48 is slightly greater than the outside diameter 24 of the machined shank 16 of the S cam member 12 in order to rotationally support the S cam member 12. Accordingly, the inside diameter 48 of the bushing member 40 may be 0.001 to 010 inches greater than the outside diameter of the machined shank 24 and is preferably 0.002-0.005 inches greater than the outside diameter of the machined shank 24.

The tubular body 44 has a length 50. The length 50 is substantially coextensive with a significant portion of the length of the shank 16. Accordingly, when the bushing member 40 is disposed on the S cam member 12, the bushing member 40 extends from proximate the S-head 14 to proximate the splines 18. The bushing member 40 is preferably made of plastic material, although other compositions, including metal having suitable wear characteristics may also be used.

The bushing holder 42 is formed generally of a thin walled tubular body 52. The tubular body 52 has an outside margin 54 a defined in part by a diameter 54 and an inside margin 56 a defined in part by an inside diameter 56, as depicted in FIG. 1 b. A minimal annular space is defined between the outside margin (defined in part by the diameter 46) of the bushing member 40 and the inside margin 56 a of the bushing holder 42. The bushing member 40 is preferably press fit into the bushing holder 42.

In a preferred embodiment, as depicted in FIG. 2, at least one spiral groove 58 and preferably two intersecting spiral grooves 58, 58 a are defined in the surface 56 a. Additionally, two circumferential grooves 60 a, 60 b are preferably defined in the surface 56 a. Each of the respective grooves 60 a, 60 b intersects the single spiral groove 58 or both of the intersecting spiral grooves 58, 58 a. A threaded fitting bore 62 is defined through the tubular body 52 and intersects each of the circumferential grooves 60 a, 60 b, respectively. A grease fitting 64 is preferably threaded into each of the threaded fitting bores 62. A suitable lubricant forced through the respective grease fitting 64 fills the respective circumferential groove 60 a, 60 b and then travels along the path of intersection spiral groove 58 or grooves 58, 58 a to ensure that the minimal annular space defined between the inside diameter 56 of the bushing holding 42 and the outside diameter 46 of the bushing member 40 is substantially filled with lubricant.

End seals 66 are disposed in each end of the tubular body 52 proximate the respective end margins of the bushing member 40. The outside margin 70 of the respective end seals 66 closely engages the inside margin 56 a of the tubular body 52. The inside diameter 72 of the end seals 66 is such that the end seal 66 closely engages the machined outside margin 24 of the shank 16 of the S cam member 12. The respective end seals 66 in cooperation with the bushing holder 42 and the machined shank 24 of the S cam member 12 cooperate to effect the environmental isolation of the bushing member 40.

Brackets 68 may be welded to the exterior margin of the tubular body 52. Each of the brackets 68 has suitable bores (four bores in FIG. 1) defined therein to be brought into registry with bores defined in an axle mount 74. The axle mount 74 is preferably welded to the axle of the vehicle. Suitable bolts may then couple the respective brackets 68 and axle mounts 74 for mounting the S cam assembly 10 to the vehicle. It is understood that different types of axles currently in use in the commercial truck market may require different means of affixing the S cam assembly 10 to the vehicle. Accordingly, one or both of the ends of the tubular body 52 may be welded to a vehicle component, thus eliminating the need for the bracket 68/axle mount 74.

It will be obvious to those skilled in the art that other embodiments in addition to the ones described herein are indicated to be within the scope and breadth of the present application. Accordingly, the applicant intends to be limited only by the claims appended hereto. 

1. A support assembly for supporting an S cam, the S cam being an intermediary device between a brake actuator and a set of wheel brakes and is generally formed with an elongate metal shank having an S-head at a first end of the shank and a set of splines at a second end of the shank, the S-head having at least one arm for engaging a respective brake shoe, whereby rotation of the S cam in a first direction causes the at least one arm of the S-head to act on the brake shoe to frictionally engage the brake shoe with a brake drum, the brake drum being affixed to a wheel, comprising: a single bushing rotationally supporting the S cam, the bushing extending along the S cam shank from proximate the S-head to proximate the splines, the bushing being substantially sealed within a bushing holder by a first seal member and second seal member disposed proximate first and second ends of the bushing respectively, each of the seal members forming a sealing interface with the bushing holder and the s cam shank.
 2. The support assembly of claim 1, the bushing being formed of a plastic material.
 3. The support assembly of claim 1, the bushing being substantially enclosed within the bushing holder.
 4. The support assembly of claim 3, an outside diameter of the bushing being sized to form a substantially tight fit with an inside diameter of the bushing holder.
 5. The support assembly of claim 3, the bushing holder having at least one grease fitting disposed in a bore defined through a bushing holder body for transporting lubricant to the inside margin of the bushing holder.
 6. The support assembly of claim 5, the grease fitting intersecting a circumferential groove defined in the bushing holder inside margin.
 7. The support assembly of claim 6, the circumferential groove intersecting at least one spiral groove defined in the bushing holder inside margin.
 8. The support assembly of claim 7, the circumferential groove and the at least one spiral groove defined in the bushing holder inside diameter forming a path for lubricating the interface defined between the bushing and the bushing holder.
 9. The support assembly of claim 1, an S cam shank outside margin being spaced apart from an inside margin of the bushing by an amount of between 0.001 and 0.010 inches.
 10. A support assembly for supporting an S cam, the S cam being an intermediary device between a brake actuator and a set of wheel brakes and being generally formed with an elongate metal shank having an S-head at a first end of the shank and a set of splines at a second end of the shank, the S-head having at least one arm for engaging a respective brake shoe, whereby rotation of the S cam in a first direction causes the at least one arm of the S-head to act on the brake shoe to frictionally engage the brake shoe with a brake drum, comprising: a single bushing rotationally supporting the S cam, the bushing extending along the shank from proximate the S-head to proximate the splines, the S cam shank outside margin being spaced apart from an inside margin of the bushing.
 11. A support assembly for supporting an S cam, the S cam having a generally elongate metal shank and having an S-head at a first end the shank and a set of splines at a second end of the shank comprising: a bushing holder; a single bushing rotationally supporting the S cam, the bushing being substantially enclosed within the bushing holder; and the bushing being substantially sealed within a bushing holder by a first and second seal members disposed proximate a first and a second end of the bushing respectively, each of the seal members forming a sealing interface with the bushing holder and the S cam shank.
 12. The support assembly of claim 11, the bushing being substantially coextensive with the S cam shank.
 13. The support assembly of claim 11, the bushing extending along the S cam shank from proximate the S-head to proximate the splines.
 14. The support assembly of claim 11, the bushing being formed of a plastic material.
 15. The support assembly of claim 11, an outside diameter of the bushing being sized to form a generally tight fit with an inside diameter of the bushing holder.
 16. The support assembly of claim 11, the bushing holder having at least one grease fitting disposed in a bore defined through a bushing holder body for transporting lubricant to the inside margin of the bushing holder.
 17. The support assembly of claim 16, the grease fitting intersecting a circumferential groove defined in the bushing holder inside margin.
 18. The support assembly of claim 17, the circumferential groove intersecting at least one spiral groove defined in the bushing holder inside margin.
 19. The support assembly of claim 18, the circumferential groove and the at least one spiral groove defined in the bushing holder inside diameter forming a path for lubricating the interface defined between the bushing and the bushing holder.
 20. An S cam assembly, comprising: a S cam member having a shank, the shank having a machined shank outer margin; a tubular bushing holder disposable annular to the shank; and a single S cam bushing disposable intermediate the shank machined shank outer margin and an inside margin of the bushing holder when the bushing holder is in the annular disposition relative to the shank.
 21. The S cam assembly of claim 20, the bushing being substantially sealed within the bushing holder by a first and a second seal member, the first and second seal members being disposed proximate first and second ends of the bushing respectively.
 22. The S cam assembly of claim 20, the machined shank outer margin being formed with a substantially smooth surface.
 23. The S cam assembly of claim 20, the machined shank outer margin having a uniform diameter.
 24. The S cam assembly of claim 20, the bushing member being press fit into the bushing holder member. 